J. Atmos. Sci., Vol. 56, 563-583 (1999).
Observations of carbon monoxide in the upper stratosphere and lower mesosphere from the Upper Atmosphere Research Satellite Improved Stratospheric and Mesospheric Sounder (ISAMS) are presented during the dynamically active early northern winter 1991/1992. CO mixing ratios are shown to generally increase with altitude from 30 to 70 km. Large mixing ratios are found in the Arctic winter polar region due to downward advection from the mean meridional circulation. Comparison with Ertel potential vorticity shows that high CO mixing ratios saturate the winter polar vortex. A simple chemical model is used to show that an observed tropical upper stratosphere maximum is likely due largely to methane oxidation. ISAMS CO data are compared with CO output from the Goddard Space Flight Center 3D chemistry and transport model (CTM), initialized with ISAMS CO. ISAMS and CTM horizontal distributions are similar near the stratopause, even during highly dynamic periods. Disagreement in the zonal mean vertical gradients occurs several weeks into the model run, with CTM mixing ratios biased high in the upper stratosphere outside the polar vortex and low in the stratospheric vortex and lower mesosphere. Modified Lagrangian mean diagnostics applied to ISAMS and CTM data provide insight into horizontal mixing processes during a merger of two anticyclones and massive vortex erosion.